As concrete slabs harden the concrete shrinks and cracks form. Grooves are placed in the slabs so that these cracks form along the grooves rather than form randomly throughout the slab. In small concrete surfaces, these grooves are formed by hand operated grooving trowels which push the aggregate in the concrete aside to form the groove and in the process form a thin cement layer on the surface of the groove. The groove may have to be troweled several times in order to maintain the shape of the groove. These grooves have rounded edges and may also have flattened areas by the grooves left from the trowels. These rounded edges are aesthetically pleasing to many people and reflect a hand finished slab of concrete.
On large slabs of concrete, hand troweling of grooves is impractical. The hand troweling of the grooves must be done while the concrete is soft enough for the trowel to push the aggregate aside, and at that stage the concrete is not hard enough support the weight of the person troweling the groove. It is impractical to support people over large slabs of concrete to perform the troweling. Repeatedly troweling the grooves is also expensive, and for large slabs of concrete the costs are further increased.
For large slabs of concrete, the grooves are cut in the concrete by saws using thin, rotating cutting blades that cut through the aggregate. These cuts were historically made the day after the concrete was poured and after the concrete had set enough to walk on it without leaving indentations in the concrete surface. These grooves were formed by large saws using concrete-cutting discs that cut thin grooves in the concrete. More recently the cutting of grooves has been used where the concrete is cut by rotating saw blades at the time of finishing or within a few hours of finishing the concrete surface. This early cutting requires special saws and blades in order to avoid unacceptably damaging the concrete surface, but the earlier cut grooves control cracks better than the prior practice where the concrete is cut the next day. Such systems use the teachings of U.S. Pat. No. 4,769,201.
When the concrete is cut by saws the grooves are typically small in width, about 0.1 inch (2.5mm), and have square corners. The wider the groove, the greater the amount of concrete that has to be removed and that takes a larger saw, takes a longer time, and wears out the expensive cutting blades faster. Further, the wider the groove the greater the likelihood that the square edges on the groove will crack, chip and spall.
These square corners that occur on machine cut grooves lend themselves to cracking or chipping easier than the rounded corners formed by the trowels. The square corners also do not appear as aesthetically pleasing to many people as do the rounded corners. Further, the square corners do not give the appearance of hand finishing as do the troweled corners.
Blades having an inverted T shape have been used to cut sealant wells in concrete, but these grooves have the deficiencies discussed above with the square corners and appearance of a machine cut groove. Some concrete saw blades have opposing sides slanting toward each other to form a V shaped groove are used to place an inclined surface on a previously cut groove. These blades have sharp corners that suffer from the same problems as the square corners, but to a slightly smaller degree.
There remains a need for a fast, economical way to provide concrete surfaces, especially large concrete surfaces, with grooves that appear to have been formed by hand trowels.